Wireless networks 100 are becoming increasingly important worldwide. Wireless networks 100 are rapidly replacing conventional wire-based telecommunications systems in many applications. Cellular radio telephone networks (“CRT”), and specialized mobile radio and mobile data radio networks are examples. The general principles of wireless cellular telephony have been described variously, for example in U.S. Pat. No. 5,295,180 to Vendetti, et al., which is incorporated herein by reference. There is great interest in using existing infrastructures of wireless networks 100 for locating people and/or objects in a cost effective manner. Such a capability would be invaluable in a variety of situations, especially in emergency or crime situations. Due to the substantial benefits of such a location system, several attempts have been made to design and implement such a system. Systems have been proposed that rely upon signal strength and triangulation techniques to permit location include those disclosed in U.S. Pat. Nos. 4,818,998 and 4,908,629 to Apsell et al. (“the Apsell patents”) and U.S. Pat. No. 4,891,650 to Sheffer (“the Sheffer patent”). However, these systems have drawbacks that include high expense in that special purpose electronics are required.
Furthermore, the systems are generally only effective in line-of-sight conditions, such as rural settings. Radio wave multipath, refractions and ground clutter cause significant problems in determining the location of a signal source in most geographical areas that are more than sparsely populated. Moreover, these drawbacks are particularly exacerbated in dense urban canyon (city) areas, where errors and/or conflicts in location measurements can result in substantial inaccuracies.
Another example of a location system using time difference of arrival (TDOA) and triangulation for location are satellite-based systems, such as the military and commercial versions of the global positioning satellite system (GPS). GPS can provide accurate position from a time-based signal received simultaneously from at least three satellites. A ground-based GPS receiver at or near the object to be located determines the difference between the time at which each satellite transmits a time signal and the time at which the signal is received and, based on the time differentials, determines the object's location. However, the GPS is impractical in many applications. The signal power levels from the satellites are low and the GPS receiver requires a clear, line-of-sight path to at least three satellites above a horizon greater than about 60 degrees for effective operation. Accordingly, inclement weather conditions, such as clouds_, terrain features, such as hills and trees, and buildings restrict the ability of the GPS receiver to determine its position. Furthermore, the initial GPS signal detection process for a GPS receiver can be relatively long (i.e., several minutes) for determining the receiver's position. Such delays are unacceptable in many applications such as, for example, emergency response and vehicle tracking. Additionally there exists no one place that this location information is stored such that a plurality of wireless devices 104 could be located on a geographic basis.
Summary of Factors Affecting RF Propagation
The physical radio propagation channel perturbs signal strength, causing rate changes, phase delay, low signal to noise ratios (e.g., ell for the analog case, or Eb/no, RF energy per bit, over average noise density ratio for the digital case) and doppler-shift. Signal strength is usually characterized by:                Free space path loss (Lp)        Slow fading loss or margin (Lslow)        Fast fading loss or margin (Lfast)        
Loss due to slow fading includes shadowing due to clutter blockage (sometimes included in 1.p). Fast fading is composed of multipath reflections which cause: 1) delay spread; 2) random phase shift or rayleigh fading, and 3) random frequency modulation due to different doppler shifts on different paths.
Summing the path loss and the two fading margin loss components from the above yields a total path loss of:Ltotal=Lp+Lslow+Lfast 
Referring to FIG. 3, the figure illustrates key components of a typical cellular and PCS power budget design process. The cell designer increases the transmitted power PTX by the shadow fading margin Lslow which is usually chosen to be within the 1-2 percentile of the slow fading probability density function (PDF) to minimize the probability of unsatisfactorily low received power level PRX at the receiver. The PRX level must have enough signal to noise energy level (e.g., 10 dB) to overcome the receiver's internal noise level (e.g., −118 dBm in the case of cellular 0.9 GHz), for a minimum voice quality standard. Thus in the example PRX must never be below −108 dBm, in order to maintain the quality standard. Additionally the short term fast signal fading due to multipath propagation is taken into account by deploying fast fading margin Lfast, which is typically also chosen to be a few percentiles of the fast fading distribution. The 1 to 2 percentiles compliment other network blockage guidelines. For example the cell base station traffic loading capacity and network transport facilities are usually designed for a 1-2 percentile blockage factor as well. However, in the worst-case scenario both fading margins are simultaneously exceeded, thus causing a fading margin overload.
Detailed Description of the Prior Art
Turning to FIG. 1 is a typical second-generation wireless network 100 architecture designed for a code division multiple access (CDMA) and is similar for a time division multiple access (TOMA) or others such as GSM. These are all digital systems that may or may not have the ability to operate in an analog mode. A general overview of the operation of this system will begin when the wireless device user 102 initiates a call with the wireless device 104. A wireless device 104 may take the form of a wireless device 104, personal digital assistant (PDA), laptop computer, personal communications system, vehicle mounted system, etc. Radio frequency (RF) signal 106 is sent from the wireless device 104 to a radio tower and base-station transceiver subsystem (BTS) 300 (FIG. 3), having a global positioning system (GPS) receiver 110-A, 110.8, or 110-C as part of the BTS. The GPS receiver 302 (described in FIG. 3) receives a GPS satellite network signal 112 from the GPS satellite network 114, used by the radio tower with network BTS 108 for timing information. That information is used by the BTS to synchronize the communications signal and allow decoding of the digitized wireless device 104 radio frequency signal 106. The call is then carried from the radio tower and BTS with GPS receiver 110⋅A, 110-B, or 110-C through a wired link 116 via a T1, T3, microwave link, etc, to the base station controller (BSC) 118-A with vocording 120, CIS 122, and a backhaul l/F 124, where the call is formatted and coded into data packets by the BSS manager 126 via an intersystem logical connection 128. The call is then sent to the switch 130 via intersystem logical connections 132, where the call is then forwarded through intersystem logical connections 150 to the PSTN 138. The call may also be directly routed to another wireless device 104 on the wireless network 100.
From the PSTN 138, the call is forwarded through a connection from the PSTN 138 to communications link 140 and then to land lines 142. As the call proceeds, the words or data from the wireless device user 102 and the ultimate person or device at the receiving end of the call, are formatted, coded and decoded again and again, in the manor described above, throughout the conversation as the conversation or data volleys back and forth. Turning to FIG. 2 is a typical third generation (3G) wireless network 200. The only major difference between the second generation wireless network 100 and third generation wireless network's 200 architecture is the addition of a packet data service node (PDSN) 202 and in the inner system logical connection 204 which connects the PDSN 202 to the BSC 118-B. However, it should be noted that the expansions in architecture do not affect current implementation of this machine and/or process as described by this patent. The methodology is the same as in the second generation wireless network 100 (FIG. 1) and for completeness the periphery 3G 200 components and their logical locations have been shown.
As other technologies in network design emerge, it is important to realize that modifications and improvements can be made to this design and patent while retaining the spirit in which it was written. FIG. 1 and FIG. 2 demonstrates the logical locations in which this patent applies to current technology. It is both obvious and required that some changes would have to be made to accommodate future technologies and again are understood to be within the spirit of this patent.
Ability to Locate Wireless Device
There are numerous methods for obtaining the location of a wireless device 104, which have been taught in the prior art. Most common are in wireless networks (CDMA, TOMA, GSM, etc). All of these wireless networks 100 currently use similar hardware, which these patented location methods take advantage of.
Referring now to FIG. 3, details of a typical three sector radio tower 110-A. The BTS 300 with a GPS receiver 302 are shown. This radio tower 110⋅A exists in most current wireless networks 100 (FIG. 1) and 200 (FIG. 2) and is used most commonly. Its inclusion is for completeness of this document.
Still referring to FIG. 3, the typical three sector radio tower 110-A with BTS 300 setup includes a BSC 118-A, and 118-B which is connected to a BTS 300 through a T1 116 or a microwave link 304. The GPS has a receiver 302 that is used in its operation to establish timing information for communication synchronization. The radio tower 110-A has 3 sectors. Each sector comprises one primary receive antenna 306-A, 308-A, 310-A, and one diversity receive antenna 306-C, 308-C, 310-C. Each sector also has one transmit antenna 306-B, 308-B, 310-B. These receiver antennas and transmit antennas are elevated by the radio tower pole 312 and connected to the BTS by antenna leads 314.
FIG. 4 illustrates the typical footprint characteristics (side view) of a typical threesector radio tower antenna 110-A, such as described in FIG. 3. Each sector has a primary lobe 400 (which corresponds with its primary directivity), multiple side lobes 402-A and 402-B, and multiple rear lobes 404.
FIG. 5 illustrates the typical footprint characteristics (top view) of a typical threesector radio tower antenna 110-A, such as described in FIG. 3. Each sector has a primary lobe 400 (which corresponds with its primary directivity), multiple side lobes 402-A, and 402-B, and multiple rear lobes 404.
Location Determined as Follows:
As many other patents go into great depth on location-based methods, for completeness, a brief description of the methods preferred by this patent will be discussed.
FIG. 6 shows general methods for triangulation with three radio towers; 110-A, 110-B, and 110-C. This method is covered in numerous other patents but the basic idea is included for completeness.
Still referring to FIG. 6 round trip delay (RTD) from each radio tower and BTS 110-A, 110-B and 110-C is used to calculate distance from radio towers to the wireless device 104. To calculate distance 600-A, 600-B, and 600-C, take the RTD (unit in seconds) and multiply by the speed of light (or speed in relative medium of propagation) and divide by two.RTD*c/2·D,D=Distance in meters from tower(c=speed of light)Having done so, you can calculate the position, relative to the known geological position of the towers 110-A, 110-B, and 110-C, of the wireless device 104.
To calculate position you find the intersection of three concentric spheres around each radio tower and BTS 110-A, 110-B, and 110-C with each radius equaling the distance 600-A, 600-B, and 600-C to the wireless device 104 from that radio tower and BTS. The wireless device 104 location is the intersection of the three spheres.
FIG. 7 shows a two-tower location finding method as taught in the prior art. It is included for completeness of this document. It uses two towers 110-A, and 110B with a wireless device 104 at distances of 700-A, and 700-B.
Because each tower has more than one sector, as the wireless device 104 approaches a radio tower 110-A or 110⋅B, it may be talking to more than one sector on a single radio tower as is illustrated in FIG. 4, FIG. 5, and FIG. 6. When this occurs, there is a critical distance below which the time it takes for two sectors on a single tower to reach the wireless device 104 is indistinguishable due to hardware calculation limitations. This would make the distance from both sectors (which are already very close, being located on the same tower) appear the same. In this case you should regard the tower as having only one sector, characterized by the distance (equal) from the two sectors. Now, using this as a base you can calculate the location at the wireless device 104 by examining the intersection on the two spheres (one from each tower) and the intersection of the vertical plane between the two towers 110-A and 110-8. This should result in a single point and hence the location of the wireless device 104.
FIG. 8 shows a one-tower 110-A location method. It shows a tower (3 sectors) and three distances 800-A, 800-8, 800-C from a wireless device 104.
In this case, the wireless device 104 has approached a radio tower 110-A so closely that is talking to three sectors on the site. Because, at this proximity, the distance 800-A, 800-B and 800-C between the three sectors (Sector 1, Sector 2, and Sector 3) on the radio tower 110-A is so negligible, the accuracy is reduced to predicting the wireless device's 104 location with one concentric sphere around the radio tower 110-A, with a radius equaling the distance 800-A, 800-8, or 800-C from any site as calculated above. Relative direction can be computed using the sector (Sector 1, Sector 2, or Sector 3) with the strongest receive power from the wireless device 104 as the likely direction to the wireless device 104 (assuming highly directive antennas are being used).
The problem with these methods is that they do not disclose a means for formatting and structuring the decoded data from a plurality of wireless devices 104 into a database or other means of collaboration of data. This database could create a universal standard that could be accessed by other applications such as navigation apparatuses; wireless networks 100 for network tuning purposes; or many other applications.